1. Field of the Invention
The invention concerns a circuit arrangement for the wireless transmission of a control signal to the control path of a controlled semiconductor valve, particularly a thyristor, which can be used preferably for a converter for high voltage.
2. Description of the Prior Art
A control signal from a control signal transmitter is always transmitted to the control path of a controlled semiconductor valve by wireless means, i.e., electrically separated, if a particularly large potential difference exists between the control signal transmitter and the semiconductor valve, if there is a particularly large or small distance between them, if both are poorly accessible, or if the control signal transmitter and the semiconductor valve move relative to each other.
A circuit arrangement of the kind mentioned above is known from the German Offenlegungsschrift No. 1,916,875. This involves a speed control device for an electric machine. Here, the rotating armature winding can be short-circuited via a receiver which contains electronic switching elements. The transmitter is positioned at the stationary exciter. It is possible to use as the transmitter for the control signal a light source (e.g., an incandescent lamp, light-emitting diode) and as the switching element for controlling the armature current a light-controlled electronic component (e.g., a phototransistor, photothyristor). However, the control signal can also be transmitted electromagnetically, e.g., by means of a transformer, the primary winding of which is arranged as the control signal transmitter and whose secondary winding is arranged in the control circuit of a component of the receiver, or by means of a magnet as the control signal transmitter and a magnetic field-controlled semiconductor resistor as the receiver. It is also possible to transmit the control signal electrostatically.
A circuit arrangement of the kind mentioned above is also known from the German Patent No. 1,538,099. This concerns a firing circuit for a controlled semiconductor valve. This firing circuit is designed so that it derives the firing energy from the voltage at the anode-cathode path of the semiconductor valve. In this arrangement, a pulse capacitor which can be discharged by means of an auxiliary switch on to the control electrode-cathode path of the semiconductor valve, is charged by means of this voltage. For the auxiliary switch a light-controlled thyristor is provided which can be triggered by light radiation from a light source. The light source is considered here as the control signal transmitter. It may be arranged at some distance from the semiconductor valve. This firing circuit is particularly well suited for a thyristor which is arranged, possibly in series with other thyristors, in a converter for high voltage.
The known circuit arrangements therefore make use of a light-optical, electromagnetic or capacitive transmission of information in the wireless transmission. With light-optical transmission, dirt which settles on the optical components in the transmission path can be a disturbance in the long term. With electromagnetic transmission, as well as with capacitive transmission, one is in general tied to a short coupling distance between the control signal transmitter and the semiconductor valve, which is frequently not permissible, however, for reasons of a large potential difference, or is not possible in the case of rotating machines.
A circuit arrangement for the wireless transmission of a control signal to the control path of a controlled semiconductor valve, in which the control signal is provided for modulation of a high-frequency transmitter, which is arranged at some distance from a high-frequency receiver containing a demodulator whose output signal is fed to the control path of a semiconductor valve, is the subject of another application on file in the United States Patent Office, the assignee of which is the same as the assignee of this application.
In such a circuit arrangement it is important to determine whether during the operation of the controlled semiconductor valve a short-circuit has occurred in its anode-cathode path. If several such semiconductor valves are combined in a converter, for instance, it is also of interest to learn how many and which semiconductor valves have failed.
It is an object of the invention to provide a circuit wherein a return message regarding the failure of one or possibly several semiconductor valves is available with little technical and apparatus expenditure on the transmitter side.